In U.S. Pat. No. 4,042,036, an electrical impact tool particularly adapted for driving nails utilizes one stationarily mounted and one pivotally mounted motor and rotating flywheel assembly, with the pivotally mounted flywheel being moved toward a ram and pushing the ram against the stationarily mounted flywheel, The flywheels are rotated in opposite directions, such that engagement of each with the ram will drive the ram in the desired direction. Each motion is produced by a movable nosepiece which is pushed into engagement with the work. U.S. Pat. No. 4,323,127 discloses a pair of pivotally mounted, motor driven flywheels moved essentially simultaneously into engagement with a ram disposed between them, as by a solenoid whose force is enhanced by a linkage system having a higher mechanical advantage at the start of movement, which offsets the lower pull of the solenoid at the start of movement. The ram is provided with a taper on each side at the end initially engaged by the flywheels, so as to cause the flywheels to be wedged apart as the ram movement starts, thereby increasing the compressive forces of the ram against the flywheels and enhancing the force transmitted by friction between the flywheels and the ram. The housing in which the ram and flywheels are mounted is provided with one or two tension rods which connect the pivot mounts of opposed flywheels, in order to equalize precession forces and also to withstand other forces exerted in opposite directions against the flywheels by the ram, without increasing the weight of the housing.
The ram is returned to its initial position by an elastic shock cord, also known as a bungee cord, which is composed of numerous elastomer fibers enclosed within a sheath which appear to be more capable of repeated extensions and retractions than a coil spring, for instance, without failing due to repetitive stress. Although the impact device disclosed by this patent is highly effective, the weight of two motors, in a hand held tool particularly adapted to drive nails and the like, leaves room for improvement. In addition, the friction material, with which the sides of the ram previously are provided, such as brake lining, is highly effective for a period of time, but ultimately is subject to undue wear. In addition, a direct drive between a motor and flywheel causes the motor to reduce speed when the flywheel is reduced in speed, due to loss of inertia through transmission of a driving force to the ram. The necessary capacity for acceleration of the motor, to bring the flywheel up to the desired speed for the next operation, has resulted in an undue expense for a tool which is to be marketed in large quantities.
Among the objects of this invention are to provide an impact tool the weight of which may be reduced by utilizing a single motor to drive a pair of flywheels; to provide such a tool in which a sequence of operations may be carried out in a shorter period of time, through enhancing the accelerating capacity of a drive motor by providing a drive connection means between the drive motor or rotative drive means, such that the speed of the motor is not reduced in proportion to the reduction of speed of the flywheels due to loss of inertia in imparting driving force to a ram; to provide such an impact tool in which the drive to each of a pair of pivoted flywheels is through a pulley and belt arrangement, in which the distance between the pulleys is decreased as the flywheels engage the ram, so that the coupling between the belts and the flywheels will lessen, and a reduction in speed of the flywheels will not be reflected to the same extent in the speed of the drive means; to provide such an impact tool in which the tension members connecting the pivot points of opposed pivotal flywheels are formed integrally with opposed housing plates, thereby reducing the cost of construction, particularly assembly of the tool; to provide such an impact tool in which a drive and two separate flywheels may proceed from a single motor or other driving means, as through intermeshing and oppositely. rotating gears, only one of which is driven by the motor or drive means; to provide such a tool which is light in weight, fast in operation and is long wearing and has an extended life.